A process for the manufacture of a symmetrical, terminally ring-substituted polyenes by reacting a polyene di(O,O-dialkyl acetal) with a cyclic dienol ether in the presence of a Lewis or Brönsted acid, hydrolyzing the condensation product resulting therefrom and cleaving off alcohol under basic or acidic conditions from the polyene derivative produced at this stage. The novel cyclic dienol ethers, as well as, novel intermediates resulting from the condensation and additional intermediates in this process form further aspects of the invention. The final products are primarily carotenoids, which find corresponding use, e.g., as colorings and pigments for foodstuffs, animal products, etc.
The claimed invention relates to cyclic dienol ethers of formula (III).
wherein R3 is hydrogen and R4 is C1-4 alkoxy or R3 and R4 together form an optionally substituted methylenedioxy group —O—C(R5)(R6)—O—, wherein R5 and R6 are each independently hydrogen, C1-4 alkyl or phenyl.